The invention relates to a thermally-responsive record material. It more particularly relates to such record material in the form of sheets coated with color-forming compositions comprising chromogenic material (electron-donating dye precursors) and acidic color developer material. The invention particularly concerns a thermally-responsive record material (thermal record material) capable of forming a substantially non-reversible image with improved color-forming efficiency and/or image density.
Thermally-responsive record material systems are well known in the art and are described in many patents, for example: U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318; and 4,470,057 which are incorporated herein by reference. In these systems, basic chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark.
Carbamate compounds are known (See. U.S. Pat. No. 4,095,034, U.S. Pat. No. 4,260,781, U.S. Pat. No. 4,301,087 and U.S. Pat. No. 4,443,621). None of these patents teach thermally-sensitive color-forming compositions containing carbamates or suggest that their respective U.S. Pat. No. 4,443,621). None of these patents teach thermally-sensitive color-forming compositions containing carbamates or suggest that their respective carbamates can be used as components of a thermally-sensitive color-forming composition. Igarishi et al's, Mechanisms of Color Formation on Thermo-Sensitive Paper, Scientific Publications of the Fuji Photo Film Co., Ltd., No 29, 97 (Advances in Non-Impact Printing Technologies for Computer and Office Application, Proceedings of the First International Congress, Venice, Italy, Jun. 22-26 (1981)) discusses certain mechanisms of color formation of a very specific thermo-sensitive paper referred to as "NCR type". The reference discloses that dodecyl-N-phenylcarbamate can be used as a sensitizer to increase the sensitivity of paper, "so that the recording density at the same recording energy is three or four times higher than in ordinary paper" (page 98). Stearylamide can also be used with less success. Dodecyl-N-phenylcarbamate is the only carbamate discussed by the reference and there is no discussion about how structurally different carbamates would function.
Thermally-responsive record materials have characteristic thermal responses, desirably producing a color image upon selective thermal exposure.
In the field of thermally-responsive record material, thermal response is defined as the temperature at which a thermally-responsive record material produces a colored image of sufficient intensity (density). The desired temperature of imaging varies with the type of application of the thermally-responsive product and the equipment in which the imaging is to be performed. The ability to shift the temperature at which a satisfactorily intense thermal image is produced for any given combination of chromogenic material and developer material is a much sought after and very valuable feature.
The ability of a thermally-responsive record material to have improved imaging characteristics such as enhanced image intensity, image density, or improved thermal response, would be an advance in the art and of commercial significance.